I’m not sure when it opened up, but this morning, I was able to enter my address at https://fiber.google.com and sign up for service. I received a confirmation email, and it included the message below.
“We’re getting ready to bring you service, which may include exterior installation or construction work. We’ll contact you when it’s time to set up your in-home installation appointment. Please be aware that it may be a while before we can complete your installation, so we suggest that you keep a way to access the web until Fiber is up and running.”